How do lymphocytes differ from red blood cells visually?

Lymphocytes can be visually identified by their distinct appearance which includes a dark blue nucleolus surrounded by a pale blue cytoplasm. This characteristic helps differentiate them from red blood cells, which do not have a nucleus and typically appear as bright red due to the presence of hemoglobin. The visual contrast in color and the structure of the nucleus in lymphocytes are key features that allow for easy identification under a microscope.

The nucleus of a lymphocyte is relatively large and takes up a significant portion of the cell, giving it a more prominent appearance compared to the biconcave disc shape of red blood cells that lack a nucleus altogether. This structural difference is critical in the functioning of these cells, as lymphocytes are key components of the immune system, while red blood cells are primarily responsible for oxygen transport.